A light pipe is a typically cylindrical, transparent structure through which light is channeled or transmitted along the longitudinal axis of the light pipe by total internal reflection. Total internal reflection prevents the light from passing from inside the light pipe to outside of the light pipe. Total internal reflection occurs when light impinges on an interface between the light pipe and the atmosphere surrounding the light pipe at an angle that is greater than a critical angle. The critical angle is a function of the indices of refraction for the medium of the light pipe and the medium of the surrounding atmosphere.
The light transmitted by light pipes is generated by a light source. The light source is usually contained in a lamp assembly to which the light pipe is fastened. A typical lamp assembly includes a housing that contains a light source such as a light emitting diode (“LED”). The light pipe should be secured to the lamp assembly to prevent accidental separation of the light pipe from the lamp assembly. In many applications where light pipes are used, the space to accommodate the light pipe and associated lamp assembly is limited. For example, the space available for the light pipe and lamp assembly in interior automobile lighting may be limited. Therefore, typically very little space is available for structures and features that secure the light pipe to the lamp assembly. Current known securing structures include mechanisms such as clamps and epoxies. But, because the light pipe typically has a smooth, cylindrical exterior, the light pipe may easily disconnect from a lamp assembly when known securing structures are used to secure the light pipe to the lamp assembly.
Known light pipes include a white strip or other surface element on the light pipe or inside the light pipe that reflects light impinging on the surface element. At least some of the reflected light strikes the interface between the outside surface of the light pipe and the surrounding atmosphere at an angle that is less than the critical angle of the light pipe-atmosphere interface. This light emanates from the light pipe as emitted light. In order to direct the reflected light in the proper direction, the strip or surface element need to be properly aligned with respect to the lamp assembly.
As the light emanates from the light pipe, the intensity of the emitted light may decrease along the length of the light pipe. For example if too much light escapes from the light pipe in locations near a light source, the light emanating from an opposing end of the light pipe may not be as bright or intense as the light emanating from other parts of the light pipe. Such an uneven distribution of emitted light may be undesirable.
Thus, a need exists to provide a light pipe that more evenly emits light along the length of the light pipe. Moreover, a need also exists for a coupling between the light pipe and lamp assembly that orients the light pipe with respect to the lamp assembly.